1. Field of the Invention
The present invention relates to an electric motor, particularly to an electric hub motor in which rotor and stator plates divided in several sections are substituted for a conventional rotor and stator plates in single pieces. Thereby cost of molding and waste material are greatly reduced and unused material of other processes is usable, resulting in a significant cost advantage.
2. Description of Related Art
In conventional art, brushless peripheral-rotor motors, in which rotors are placed outside stators, are widely used in hubs of electric vehicles and washing machines. Motors of this type have inner stators with a plurality of electric coils connected with power. During operation as an electric generator, a rotating external magnetic field results in the generation of electric current. In each motor of this type, the rotor has a larger diameter than the stator and is provided with a plurality of permanent magnets. Usually, the rotor is made of a curved rotor plate in which the stator is inserted. Various ways of placing the permanent magnets in the rotor are used, which are mainly decided by cost. Accurate positions of the permanent magnets in the rotor plate are important for proper functioning of the motor.
There are mainly two conventional methods of making rotors. In the first, a rotor body is made in a single piece on a lathe, with inner peripheral grooves being cut out. Into each of the inner peripheral grooves a permanent magnet is laid. Since cutting of the inner peripheral grooves and automatic inserting of the permanent magnets is difficult, the permanent magnets are usually glued to an inner periphery of the rotor body. This method, however, is expensive and often results in errors of production. Furthermore, since the permanent magnets are glued to metal, magnetic flux is reduced by some degree. In the second method, rotor plates are produced by punching. Using silicon steel leads to better magnetic properties and a higher magnetic flux. Several rotor plates are inserted in a casing. By the rotor having several plates, cutting grooves is facilitated and working is easy. Choosing appropriate shapes for the rotor plates results in good magnetic properties and high effectivity in conjunction with the stator coils. However, since the rotor plates have relatively large diameters, large punching machines are required, and punching produces large quantities of waste material, leading to high cost of production.